The invention relates to a method of producing a storage cathode comprising a porous, sintered body of a refractory metal, in which non-interlocking powder particles of a refractory metal are compacted to form a body, and the body is sintered.
Storage cathodes of this type are used in electron guns for electron tubes such as television tubes, picture pick-up tubes, travelling wave tubes, cylstrons etc. Tungsten and/or molybdenum are usually used as the refractory metals.
Methods of producing a storage cathode are known in which very irregularly shaped and interlocking powder particles of a refractory metal are compacted. Due to their interlocking nature, it is possible to compact such powders at low temperatures. During sintering, however, irregularities occur in the porosity of the sintered body, such as closed pores and fully dense sintered portions, which irregularities result in a loss in intensity and in uniformity of the emission. The present invention concerns methods using non-interlocking particles, wherein such irregularities occur much less frequently or not at all.
A method of the type defined in the opening paragraph is disclosed in the English language abstract of SU-654981-A from Derwent "World Patent Index". This disclosure describes a method in which tungsten powder, consisting of non-interlocking substantially spherical particles is compacted in a hydrogen atmosphere at a pressure of 0.1 to 1.0 Gpa, at a temperature from 1100.degree.-1400.degree. C. for 5 to 30 minutes. Thereafter, the compacted tungsten body is sintered in a hydrogen atmosphere at a temperature of 2000.degree. C. for 20 minutes, whereafter the tungsten body is impregnated. The disclosed method has the drawback that the tungsten powder is compacted at elevated temperature and in a hydrogen atmosphere. This requires the use of a high-pressure press in a conditioned space. Many metals are attacked by hydrogen at such high temperatures, resulting in a degradation of these metals known as "hydrogen embrittlement". Thus, the high-pressure press appropriate for this process must be made of a metal which is immune to hydrogen embrittlement. Furthermore, this process is not so suitable for mass production as the energy required for producing a cathode is great and the process takes much time.